The Childen's Hospital of Philadelphia (CHP) is a primary treatment center for children with malignant diseases. It also has been designated a Pediatric Cancer Research Center (USPHS grant No. 14489). As a member institution of the Children's Cancer Study Group (CCSG) it will pursue study and treatment of pediatric oncologic disorders via the Phase I, II and III protocols of CCSG. Chemotherapy, and possibly immunotherapy, will be utilized alone or in conjunction with surgery and/or radiation therapy, as indicated by the study protocols, in efforts to devise more effective and less toxic methods of improving survival in children with leukemia or solid tumors. Co-Investigators from Surgery, Pathology, Diagnostic Radiology, Radiation Therapy, Dentistry and Infectious Diseases will participate in the development and conduct of these studies. Through the use of the Intergroup Study mechanism, collaboration with other Cooperative Cancer Study Groups will achieve statistically valid study of the less frequently occurring malignancies.